Rear differential mystery

[QikNip]

Per Clark's catalogue there is a stamping located on the right side of the differential (near where it mounts to the transmission) that will either be: AA, AB, AC,or AD respectively denoting it as a 3:27 open, a 3.55 open, a 3:27 Posi, or a 3:55 Posi. i have wire brushed (both sides) of my diff and the only marking I found was "X33" on the drivers side but I doubt that it's meaningful regarding the internals. Clark says it may be hard to see, but in my case it's apparently invisible. Any ideas?
Rick

[joelsplace]

It is very poorly stamped and often illegible. It wouldn't surprise me to see one that wasn't stamped. They guy that had that job should be embarrassed.